1. Field of the Invention
The present invention relates to color separation systems, and more particularly to a color separation system for use in color copying apparatus.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 62-269173 discloses a color copying machine wherein the light reflected from color documents is subjected to color separation for exposing the photosensitive member to the resulting light. The disclosed color copying machine has a first half mirror for reflecting the light of one of blue, green and red colors, and a second half mirror for reflecting the light of one color as separated from the light of two colors passing through the first half mirror. The light of each color passes through one of different optical paths and reaches a particular photosensitive member. The optical path for the light reflected from the first half mirror is provided with a transmission filter for blocking the light of color to be passed through the first half mirror.
Accordingly, the color separation optical system of the color copying machine comprises the combination of a reflection filter and a transmission filter as the half mirror, whereby the ripple produced by the reflection filter can be blocked by the transmission filter.
However, for the transmission filter to exhibit improved spectral characteristics, the filter needs to have an increased number of film layers when in the form of an interference filter or to be larger in film thickness when in the form of an absorption filter. The interference filter increased in the number of film layers, is costly and has the drawback of being prone to separation between the film layers, while the absorption filter, of larger film thickness, encounters difficulty in forming a uniform film and has the drawback of being low in optical efficiency.